1. Field of the Invention
The invention relates to a catalyst based on titanium oxide and/or zirconium oxide for decomposing HCN in gases and also to a process for decomposing HCN in gases.
2. Description of the Background
Numerous hydrocarbon-containing gas mixtures, such as, for instance, the gas mixtures obtained in the gasification of coal or oil or other hydrocarbon-containing substances, have to be freed of acid gas constituents such as H.sub.2 S before they are further processed. The H.sub.2 S removal is customarily, particularly in the case of low H.sub.2 S contents, carried out by gas scrubbing using a chemically or physically active solvent. Since HCN present in the gas mixture is dissolved by the solvents customarily used and because HCN is not completely removed from the solvent in the regeneration of the solvent, the result is HCN enrichment of the solvent, often even decomposition of the solvent by HCN. HCN is therefore removed by catalytic decomposition in a manner known per se prior to acid gas scrubbing.
Furthermore, in many industrial processes it is desirable to decompose HCN in gases without in the process catalyzing other reactions than the HCN decomposition in the gas.
The as yet unpublished, German Patent Application 43 19 234 teaches a process for removing HCN from gas mixtures containing at least HCN and sulfur compounds, particularly from gas mixtures obtained by partial oxidation or gasification of coal or oil. The process is the catalytic decomposition of HCN, with the gas mixture being brought into contact with a catalyst which decomposes the HCN by hydrogenation and/or by hydrolysis. COS present in the gas mixture is at least partially decomposed by hydrolysis over this catalyst. In particular, catalysts are employed in which the catalyst support is on titanium oxide and/or zirconium oxide. Chromium trioxide is a further catalytically active component.
Catalysts containing chromium trioxide can present problems in their preparation and disposal because of the high toxicity of chromium trioxide, since strict safety and environmental protection obligations have to be met when handling chromium trioxide. Furthermore, the catalysts of the prior art have an activity which is too low, so that either large reactor volumes or high reaction temperatures are required. A need, therefore, continues to exist for a catalyst of improved activity for the removal of HCN from HCN containing gases.